Currently only GET requests are supported as data source. A 3rd party systems use POST request to provide data.
This is also needed for connecting to graph databases like Noe4j. Noe4j only accepts http post requests and it's not a trivial task for folks to write, edit, and debug an advanced Power Query script to make the post request. Since there is currently no support for R or Python packages for Neo4j either, the only method for accessing a Neo4j database in Power BI is through the http post API, if you want to have Power BI Online Service refresh data from Neo4j. Same for using the On-Premises Data Gateway going against custom web api apps. Several of my clients exclusively use http post api's to access on-prem systems data, and it's just tough to build that for most folks in Power Query. Come to think of it, the same goes with the Bing Maps service - that's also an http post rest api call too. So many examples.
